Using HTX-rats with congenital hereditary hydrocephalus, we used neuropathological methods, including quantitative Golgi study and neurobehavioral evaluation, to investigate the following problems. (1) What kind of damage does congenital hydrocephalus cause to developing brain tissue? (2) How much can the damage be repaired by ventriculoperitoneal shunting if performed at 4 weeks of age, enabling 4-week-old hydrocephalic rats to survive beyond sexual maturation? (3) What is the status of learning ability of long-term surviving rats with arrested shunt-dependent hydrocephalus? The findings of our study suggest that congenital hydrocephalus impairs the development and formation of the dendrites and spines of the cerebrocortical neurons. Following ventriculoperitoneal shunting, we confirmed that rats with arrested shunt-dependent hydrocephalus demonstrated learning disability in a light-darkness discrimination test using a Y-maze. The development of the dendrites and spines of the cerebrocortical neurons seemed to take place to some degree after shunting, but normal spine density could not be restored. Also suggested was a possible relationship between learning disability and a decrease in spine density, i.e., impairment of synaptogenesis.